1. Field of the Invention:
The present invention relates to an apparatus for and method of determining the liquid coolant level in a nuclear reactor.
2. Description of the Prior Art:
Monitoring of coolant within a nuclear reactor is vitally important to insure proper operation of the reactor. The nuclear reactor must be continually cooled by a liquid coolant to prevent such catastropic results, such as "melt down". The importance of coolant was dramatically illustrated by the recent "Three Mile Island" disaster. Presently, it is difficult to accurately measure a liquid coolant inventory within a nuclear reactor.
Using the thermal characteristics of a liquid to determine its level has been disclosed in U.S. Pat. Nos. 2,279,043, to Harrington, 2,702,476, to De Boisblanc, and 3,280,627, to Cousins et al. In these references a number of thermocouples are vertically distributed within a container and are used to sense the temperature at different levels in the container. An electrical heater element is located adjacent to the thermocouples, and provides a uniform source of heat along the entire line of thermocouples. Heat from the heat source transfers more readily into liquids so that the temperature at a thermocouple covered by liquid is less than the temperature at a thermocouple bathed only by gases and vapors. If the temperature signal at the higher thermocouples is significantly greater than the temperature signal at the lower thermocouples, the level of liquid in the container can be located where the sudden temperature increase first occurs.
In all of the disclosed liquid level thermal sensors the heater element provides a uniform heat along the entire length of the instrument. The heating element used in the present invention is a slender rod having sectional heating zones of high and low heat depending on the location of the thermocouples. Difference thermocouples are used rather than absolute thermocouples for faster response and less sensitivity to extraneous temperature noise. In addition a tube is disposed around the instrument to provide more accurate readings of the actual liquid level and not the expanded liquid level.